1. Field of the Invention
The present invention relates to magnetic-resonance imaging apparatus to be used for producing a three-dimensional scan of a human breast (MRI Mammography.)
2. Description of the Related Art
Magnetic-resonance imaging (MRI) is used in medicine to display internal organs of the human body. In this respect it is similar to X-ray "Computed Axial Tomography" (CAT-scan). The most fundamental difference is that in the case of CAT scanning the body is penetrated by X-rays, and in the case of MRI scanning the body is penetrated by a magnetic field and a radio-frequency electromagnetic field. The potential for serious harm caused by the X-rays in the case of a CAT scan is very small, but not zero. In the case of an MRI scan, the potential for harm is supposedly zero. The two methods differ substantially also in that they highlight different features of the anatomy.
One potentially very important area of application of the MRI technique is scanning of the human breast (mammography). If the recommended yearly mammogram (for women over a certain age) can be done as well or better by an MRI technique rather than an X-ray technique, the radiation "load" on the female population will be substantially reduced.
Medical MRI apparatus presently in use, typically, have a solenoid magnet or a set of coaxial coils, large enough for a human to fit inside, several "gradient" coils producing a superimposed "sweep" field and high-frequency coils designed to detect the precession of the hydrogen nucleus (proton) in the magnetic field. With the sweep field turned off, the uniformity of the main field, in the region of interest, is generally of the order of 30 parts per million for MRI apparatus designed to measure and map hydrogen density only.